. The Bell System technical journal . Fig. 7—Part of a laboratory setup as used at 4 kilomegacycles. In cases III and IV if the hybrid junction has poor balance so thatvoltage appears at C when input is applied to arm A even though B and Dare perfectly terminated, the adjusting procedure will cancel this voltageas well. Measuring accuracy will not be impaired provided the otherassumptions are fulfilled. Measuring TI—A Fitting Which Does Not Admit of MeasuringEach End Separately A piece with a configuration unsuited to the preceding technique may bemeasured by connecting it between two straight
. The Bell System technical journal . Fig. 7—Part of a laboratory setup as used at 4 kilomegacycles. In cases III and IV if the hybrid junction has poor balance so thatvoltage appears at C when input is applied to arm A even though B and Dare perfectly terminated, the adjusting procedure will cancel this voltageas well. Measuring accuracy will not be impaired provided the otherassumptions are fulfilled. Measuring TI—A Fitting Which Does Not Admit of MeasuringEach End Separately A piece with a configuration unsuited to the preceding technique may bemeasured by connecting it between two straight pieces of waveguide suchas between flanges F and G in Fig. 5. The IT due to the vector sum ofthe reflection coefficients of the coupling at one end, any irregularities andthe coupling at the other end, is measured. Due to the distance betweenthe mismatches, the vector sum will vary over the frequency band ofinterest. MEASUREMENT OF IMPEDANCE MISMATCHES 455 m. r:- IP o. 456 BELL SYSTEM TECHNICAL JOURNAL Accuracy There are three important sources of error. The first is lack of properadjustment. The second is that due to the detector attenuator third is that due to multiple reflections. Experience and care can almost eliminate the first source. The secondsource may have a magnitude of twice the detector attenuator calibrationerror. In equations (1) and (17) this is readily apparent. The evaluationof W using equations (16) introduces negligibly more error provided IFs — Wiis made large by proper choice of the magnitude of the reflection coefficientof the termination Z. The possible errors due to multiple reflections be-tween the waveguide impedance discontinuity being measured and animperfect termination are discussed in Appendix A. If the impedancepresented by the arm B of the hybrid junction is not perfect, energ>^ re-flected from the hybrid junction will be partly absorbed in the terminationand cause an error in the measurement.
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